In many applications there is a need for a coupling arrangement with the aid of which it is possible to couple and decouple rotating objects. Without limiting the generality and merely for exemplifying purposes we consider a gear system that comprises a first shaft provided with first gear wheels and a second shaft provided with second gear wheels. Each of the second gear wheels is capable of transferring torque to and from the second shaft and meshes with a corresponding one of the first gear wheels. In this exemplifying case, the gear ratio between the above-mentioned first and second shafts can be selected by locking a desired one of the first gear wheels in a torque transferring way to the first shaft and by allowing the other one or ones of the first gear wheels to rotate freely with respect to the first shaft. Therefore, there is a need for a coupling arrangement with the aid of which a desired one of the first gear wheels can be locked to the first shaft in a torque transferring way whereas the other one or ones of the first gear wheels is/are freely rotating.
A traditional coupling arrangement comprises typically collar elements each of which is capable of transferring torque to and from the first shaft and capable of sliding in the axial direction with respect to the first shaft. Each collar element comprises indentations, e.g. dog clutch teeth, capable of locking to corresponding indentations of one of the first gear wheels in a torque transferring way. Furthermore, the coupling arrangement may comprise synchronizing means, such as e.g. cone clutches, for synchronizing the rotation speeds of an appropriate gear wheel and an appropriate collar element prior to forming the torque transferring coupling between the gear wheel and the collar element under consideration. Typically, the coupling arrangement further comprises gear-shift forks for moving the collar elements in the axial direction. The outer surface of each collar element has typically a circumferential slot for the corresponding gear-shift fork. The gear-shift forks can be operated with mechanical, hydraulic, pneumatic, and/or electrical means so as to have a desired gear ratio in each situation.
A coupling arrangement of the kind described above is, however, not free from challenges. One of the challenges is related to the need to arrange the gear-shift forks so that the force directed by a gear-shift fork to a collar element is so axially directed and so symmetric with respect to the shaft that the gear-shift fork does not tend to twist the collar element. Furthermore, in some cases, the friction between the collar element and the gear-shift fork may be problematic as there can be a significant speed difference between contacting surfaces of the collar element and the gear-shift fork and thereby even a moderate friction force may correspond to a significant instantaneous heating power.